1. Field of the Invention
This invention relates generally to a suction filter with multiple filtration elements that are fed from multiple inlets for an automatic transmission.
2. Description of the Prior Art
A simple transmission suction filter has a single media layer that is crimped on the edges between the housing flanges. This design has an inherit weaknesses: its overall capacity balanced against its efficiency and pressure drop. As more efficient media have higher flow resistance, i.e., lower permeability, a single media layer filter must be quite larger to handle the required transmission flow without having an excessive pressure drop at cold temperatures when the viscosity of the transmission fluid is highest.
Most transmission suction filters use a bag filter media arrangement, which provide higher media packaging density. This allows an increased area for fluid flow, which results in a lower pressure drop and higher dirt holding capacity while maintaining high efficiency. Furthermore, bag filters can be designed to take up less overall area due to their multiple layers of contact. They do, however, require a greater thickness to support the bag arrangement.
Bag filters have been further refined to improve performance, as U.S. Pat. No. 5,049,274 discloses. There the filter element was changed to an impregnated felt that was folded into a bag and crimped on the edges between two flanges. A hole in the lower portion of the folded bag was sealed on the edges and connected to the filter suction inlet.
An alternative used in a few transmissions employs a pleated, non-planar filter element design described in European Patent EP1588753A1. A pleated design provides an increased filter media packaging density. The tradeoff, however, is two fold: a pleated filter is more expensive to manufacture, but pleated technology allows only a rectangular housing configuration.
A need exists in the industry for a suction filter that provides high media packaging density, high dirt holding capacity, high filtration efficiency, packaging flexibility for irregular shaped housings, and low cost